Active tank stabilizer for marine vessels

ABSTRACT

Active tank ship&#39;&#39;s stabilizer devices are disclosed having symmetrically positioned variable active tanks operated in cooperation by a common actuator. The tanks are arranged to permit injection or ejection of ballast liquid in a system avoiding unstabilizing secondary resonances by additively combining the effects of static and dynamic roll moments of the ballast liquid. The system may also be coupled to the ship&#39;&#39;s hull in such a manner as to counteract roll-induced disturbances of the ship about its yaw axis.

United States Patent 1151 3,698,345 Kreitner 1 51 Oct. 17, 1972 [54] ACTIVE TANK STABILIZER FOR 3,584,591 6/1971 Fournier ..1 14/125 MARINE VESSELS Primary Examiner-Trygve M. Blix [72] Inventor. Frederick J. Kreltner, Syosset, N.Y. Atwmey S. C Yeaton [73] Assignee: Sperry Rand Corporation [22] Filed: Dec. 28, 1970 [57] ABSTBACT v Active tank ship's stabilizer devices are disclosed hav- [211 App! 101648 ing symmetrically positioned variable active tanks 1 operated in cooperation by a common actuator. The 52 us. c1 ..114/12s tanks are arranged to Permit injection or ejection of 51 Int. Cl. ..B63b 43/06 ballast liquid in a System avoiding unstabilizins [58] Field of Search ..1 14/125 16 E 122 day mamas by additively mbinin8 the effects static and dynamic roll moments of the ballast liquid. [56] References cued The system may also be coupled to the ships hull in such a manner as to counteract roll-induced ED T E A NT disturbances of the ship about its yaw axis.

732,920 7/1903 Cable ..1 14/125 8 Claims, 4 Drawing Figures OOGOGO BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to stabilization of craft and particularly concerns stabilization of marine vessels through the agency of improved active tank stabilizer apparatus.

2. Description of the Prior Art Prior art systems for stabilizing a marine vessel about its roll axis have included tank stabilizers which may be classified as belonging in passive, passive-controlled, or active categories. In passive and passive-controlled tank stabilizers, the stabilizing or ballast liquid is forced from one side of the ship to the other only by the ships rolling motion. The operation of the controlled-passive tank stabilizer is enhanced somewhat by the additional use of fast acting automatic valves that regulate the timing of roll-induced liquid flow. On the other hand, in the prior art active stabilizer tank system, the stabilizing liquid is moved from side to side in the vessel by a controlled high-capacity pump capable of forcing the liquid to move against large pressure heads.

The prior passive and passive-controlled tank stabilizers, though sometimes relatively inexpensive, are well known to have relatively low performance characteristics; i.e., they can only reduce roll, never eliminate it. Furthermore, performance is additionally degraded when the natural roll period of the vessel departs from optimum, as it often does, for instance, with different types of cargo. In the case of very low frequency roll, or list, passive stabilizers can actually reduce stability to a dangerous degree. Passive, or tuned, tanks are narrowband devices and cannot be used where large variations in the natural frequency of the vessel are to be encountered. The prior art active tank stabilizers, on the other hand, have shown utility where a relatively higher degree of stabilization is required and where slow ship speeds or where docking conditions render fm stabilizers impractical.

Prior art active and other tank stabilizer systems have resonance effects whose interrelations limit ranges of usefulness of the stabilizer. In the presence of secondary resonance, the opposing static and dynamic roll moments produced by the stabilizing liquid reach equal magnitudes, so that the stabilizer exerts, no roll moment on the ships hull. Clearly, the stabilizer can serve no useful function around secondary resonance, and the power drawn is consumed in uselessly driving ballast fluid from one side of the vessel to the other.

SUMMARY OF THE INVENTION The present invention concerns active tank ships stabilizers having symmetrically disposed active tanks whose effective ballast content may be reciprocally controlled by a common actuator. The tanks are provided with means permitting injection or ejection of ballast liquid with respect to their interiors through operation of a common actuator as determined by inertially derived control signals. The configuration including the active tank ballast contents, means for varying the effective volumes of the active tanks, and means permitting ingress and egress of ballast liquid with respect to the tanks is such that deficiencies of prior art tank stabilizer devices are overcome. In particular, the

system is arranged so that the effects of the static and dynamic roll moments of the ballast fluid are advantageously used in an additive sense for coupling stabilizing torques to the ships hull. Undesired unstabilizing effects ordinarily produced when the moments are in opposite senses are prevented. The system may also be coupled to the ships hull so as, in addition, to counteract roll-induced yaw disturbances of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, partly in cross section, of

, one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, an active tank ships stabilizer system is shown in a representative marine vessel having vertical hull members 1, la, a bottom 3, a false bottom 4, and a succession of floors or decks represented by decks 5, 6, and 7 in generally parallel arrangement above false bottom 4. The embodiment of FIGS. 1 and 2 is illustrated as having common means for moving liquid ballast between storage or active tank regions 8 and 8a located at opposed sides of the marine vessel. Active tank 8, for instance, may take the form of an elongate rectangular box, some of the sides of which may be regular parts of the structure of the vessel. For example, active tank 8 may be defined in part by a vertical portion 1 of the outer hull of the vessel and by a false bottom or horizontal floor portion 4 of the vessel. Active tank 8 may be further defined by upper horizontal floor 5 and by cooperating vertical walls 9 and 10, as seen in FIG. 2. While the shape of active tank 8 is illustrated as that of a long rectangle box as seen most clearly in FIG. 2, it is to be understood that it may readily take other shapes.

A counterpart of active tank 8 is active tank 8a located on the opposite vertical portion 1a of the outer hull of the vessel, and whose structure is completed by an extension of horizontal floor portion 4, an extension of upper horizontal floor 5, and cooperating vertical walls 11 and 12 (wall 12 is not seen, but is analogous to wall 10). The component walls of active tanks 8 and 8a are each assembled so as to make tanks 8, 8a substantially leak-proof. It is understood that active tank region 8 is shown in FIG. 1 as instantaneously having substantially its maximum size, while region 8a is shown as substantially collapsed to its minimum volume. The active tanks 8 and 8a are respectively supplied with rectangular pistons or translatable walls 15 and 15a which further define the volumes of the respective active tanks 8 and 8a. It is to be noted that vertical walls 9 and 11 may be formed as a single continuing wall; vertical walls 10 and 12 may likewise constitute a single continuing wall.

Piston walls 15 and 15a are respectively affixed to ends 16 and 16a of an actuator thrust shaft 18 which controls their translation and thus the respective and relative volumes of tank regions 8 and 8a. For example, motion of actuator thrust shaft 18 is imparted at its end 16 to rectangular piston 15, whose position determines the effective volume of active tank 8. Likewise, the position of the end 16a of thruster shaft 18 determines the position of piston 15a and thus determines the effective volume of active tank 8a. It is seen that the apparatus is arranged so that when the effective volume of active tank 8 is maximum, that of active tank 8a is minimum, and vice versa.

Pistons l and 15a may be provided with well known piston rings (not shown) or other such conventional means for substantially preventing leakage of ballast liquid past, for instance, their respective interfaces with walls 4, 5, 9, and 10 and 4, 5, 11 and 12. Leakage of ballast liquid past pistons 15 and 15a may further be controlled by application of a compressed gas such as air or nitrogen in the region between pistons 15, 15a and thus to the backs of the pistons. Gas under pressure from a compressor (not shown) is forced into region 20 through appropriate piping, as discussed in further detail in the FD. Braddon US Pat. application, Ser. No. 91,774 for an Active Stabilizer for Marine Vessels, filed Nov. 23, 1970 and assigned to the Sperry Rand Corporation. Should ballast liquid leak past the various described elements for maintaining minimum ballast liquid leakage, conventional pump means (not shown) may be employed for returning such liquid to the system including active tanks 8 and 8a.

As is seen particularly in FIG. 1, an actuator is placed centrally between hull walls 1 and la and thus between active tanks 8 and 8a. Actuator 25 may be, for instance, a hydraulic actuator of generally conventional type having a piston 26 located in a closed hollow cylinder 27, piston 26 being mounted on actuator thrust rod 18. Rod 18 extends through glands (not shown) in the opposed ends of cylinder 27 and is free to translate therein. Piston 26 is driven to the right or to the left according to the sense of flow of hydraulic liquid in pipe 30 with respect to its sense of flow in pipe 30a under control of hydraulic pump 31. Pump 31 may be driven by a reversible electric motor 34, for example. Other well known directionally controllable pump and motor combinations may be substituted for pump 31 and motor 34. It is evident that multiple actuators like actuator 25 may be operated for synchronous control of the active tanks. It will be evident also that other types of actuators may be employed. For example, the average power drawn by the stabilizer may be minimized by using a conventional actuator of the type with reversible power flow. A rotary electrical actuator may be used, for instance, of the type which draws energy from the electrical power source and delivers it to the stabilizing liquid during one part of the roll cycle, and absorbs energy from the liquid and returns it to the power source during another part of the cycle.

A significant feature of the invention lies in the arrangement of the pipe or ducting system for permitting ballast liquid to flow from active tank region 8 to active tank region 8a, and vice versa, according to the sense of motion of actuator 25. Unlike conventional systems, the connection between tank regions 8 and 8a is made by a horizontal duct 40, which may be of rectangular or other shape, having an axis located well above the tank regions 8 and 8a. Duct is illustrated in FIGS. 1 and 2 as resting upon deck or floor 7, at a considerable elevation above active tank regions 8 and 8a and hydraulic ram 25 and its associated pistons 15 and 15a. In fact, it is desired to locate duct 40 as far above tank regions 8 and 8a as the geometry of the ship will v permit, for reasons which are yet to be explained. Duct 40 is connected to active tank region 8 via a first vertical duct 41, while it is connected to active tank region 8a via a second vertical duct 41a. As is seen in FIGS. 1 and 2, the walls of vertical duct 41 may comprise the wall 1 of the ships hull, an opposed parallel vertical wall 44, and connecting side walls which may simply be integral vertical extensions of walls 9 and 10 (FIG. 2). Similarly, the walls of vertical duct 41a may comprise the wall la of the ships hull, an opposed vertical wall 44a, and connecting said walls which may simply comprise integral vertical extensions of the walls 11 and 12 that partly define tank region 8a. The ducts 40, 41, and 41a are smoothly joined in a continuous path so as to reduce turbulent flow effects and may be made with smooth interiors and of generous size so as not to provide resistance to rapid flow of ballast liquid between regions 8, 8a, when such is commanded.

As previously noted, FIG. 1 illustrates one extreme condition of the apparatus. For example, in FIG. 1, actuator piston 26 has moved pistons 15 and 15a to their extreme leftward positions, electrical command signals having been applied by electrical leads 35 to motor 34 to cause pump 31 to operate, causing hydraulic liquid flow within pipes 30, 30a, as indicated by the respective arrows 36 and 36a. In FIG. 1, substantially all ballast liquid has been forced from active tank 8a through ducts or channels 41a, 40, and 41 into active tank 8, thus providing a static clockwise couple to the hull of the vessel.

In the other extreme condition of the control system, actuator 25 would move pistons 15 and 15a to their extreme rightward positions, electrical command signals having been applied to motor 34 to reverse the flow of fluid in pipes 30 and 30a. Substantially all ballast liquid would thus be forced from active tank 8 through channels 41, 40, and 41a into active tank 8a, providing a static counterclockwise couple to the hull of the ship.

It is thus seen that the embodiment of FIGS. 1 and 2 consists of an actuator 25 operating active tank pistons 15, 15a through a common thrust shaft 18. The enclosed volume behind pistons 15, 15a may contain a gas under pressure, while all of the remainder of the closed liquid system, including active tanks 8 and 8a and the return ballast transfer channels 40, 41, and 41a contains ballast liquid. Accordingly, there are no free liquid surfaces present in the closed liquid system. Forces applied by actuator 25 are determined by control signals derived from measured ship motions. As actuator 25 moves in one sense or the other from its null position, a corresponding moment is applied to the hull of the ship because of the consequent asymmetric distribution of stabilizing ballast liquid.

It is understood that the command signals applied to leads 35 are derived from sensors, such as generally indicated at in FIG. 4, which derive combinations of inertial measures or terms generally representing the instantaneous roll status of the vessel, particularly including terms which may be used to predict its immediate future status, such as roll acceleration. Such signal combinations and their manner of derivation do not necessarily form a part of the present invention. They need not be described here in detail, since suitable sensors appear in the prior art covering active ships stabilization system of various types. For example, the sensors described in the US. Pat. No. 2,979,010 to F.D. Braddon, L.F. Beach, and .I.H. Chadwick, entitled Ship Stabilization System, issued Apr. ll, 1961 and assigned to the Sperry Rand Corporation, may be employed. Reference may further be had, for example, to US. Pat. No. 2,960,959 to JQH. Chadwick and .I. Bentkowsky, entitled Roll Stabilization System for Marine Vessels, issued Nov. 22, 1960, and to US. Pat. No. 3,020,869 to L.F. Beach, entitled Activated Fin Ship Stabilizer, issued Feb. 13, 1962, both patents also being assigned to the Sperry Rand Corporation.

As noted previously, the liquid ballast channel 40 is located as far above active tank regions 8, 8a as possible. In general, active tank ships roll stabilizers operate by transferring ballast liquid between tanks located at the opposite sides of the hull of the vessel. The mechanism determining motion of the ballast liquid is controlled by inertial sensors so that ballast transfer occurs in synchronism and in proper phase relationship with respect to the ships roll motion. An asymmetric disposition of the ballast liquid in the active tanks at any one instant of time gives rise to a desirable static roll moment. However, the ballast liquid being transferred between the two tanks possesses, in addition, angular momentum about the ships roll axis; the rate of change of this angular momentum during each operat ing cycle of the stabilizer exerts a dynamic roll moment on the ship. Since maximum ballast liquid acceleration usually occurs as transfer from one active tank to the other is being completed, peak static and dynamic moments tend to coincide.

In prior art active tank stabilizers where the path of flow of ballast liquid from one active tank to the other has been placed, for example, below the active tanks, these static and dynamic moments mutually oppose each other. The magnitude of the dynamic moment increases with increasing roll frequency, while the static moment is substantially frequency independent; therefore, a frequency exists at which the static and dynamic moments substantially cancel, leaving the ship completely unstabilized. This undesired condition, referred to as the secondary resonance effect, is found to be present in many actual cases.

In the novel embodiment of FIGS. 1 and 2, the static and dynamic moments of the ballast liquid are caused to add. With the liquid ballast communication channel located above the active tank regions 8, 8a, the static and dynamic moment contributions cannot have opposing effects, and the possibility of secondary resonance is eliminated. In addition, the novel configuration yields a greater reduction in ships roll amplitude than equivalent prior art stabilizers of corresponding capacity at all finite roll frequencies. The peaking of 6 response and power demand characteristics present in the secondary resonance situation is eliminated and more effective stabilization is afforded with lower power consumption.

In the FIG. 2 embodiment, the arrow 50 indicates 6 that the flow of ballast fluid in the vertical channels 41 (or 410) is inherently vertical; in the form shown in FIG. 3, such flow may be at an angle with respect to the vertical, as indicated by arrow 150. This flow characteristic is readily induced by tilting the channel 141 at the desired angle with respect to the vertical. In this manner, the horizontal cross channel 140, placed some distance above the active tank 8 and 8a, is desirably off set from active tanks 8, 8a along the fore-aft axis of the ship, so that the moving ballast liquid has an angular momentum with a component about the ships vertical or yaw axis. Changes in angular momentum during the stabilization cycle then result in cyclic yaw moments, synchronized with the roll motion of the ship. By properly choosing the amount and direction of the fore-aft off set of return duct 140 relative to the active tanks 8, 8a, these yaw moments are made to counteract the effect of roll-induced yaw disturbances of the ship. In this manner, the configuration of FIG. 3 not only reduces roll motion of the ship without suffering secondary resonance effects, but also improves steering performance.

From the foregoing discussion of the embodiments of FIGS. 1, 2, and 3, it will be evident; that operation of the improved stabilization system is not dependent upon the location of the motive system for transferring ballast liquid. For example, a reversible pump 125, analogous to actuator 25 of FIG. 1, is shown in FIG. 4 in the elevated channel 141 coupled to vertical channels 141, 141a respectively communicating with active tanks 108, 108a. Channels 140, 141, and 141a may be placed in a vertical plane; operation of the system is then as described as in connection with FIGS. 1 and 2. On the other hand, the plane of ducts 140, 141, and 141a may be at an angle fore or aft of the vertical for the purpose of cancelling roll-induced yaw oscillations as in the apparatus of FIG. 3.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that. changes within the purview of the appended claims may be made without departure from the true scope and spirit of the invention in its broader aspects.

lclaim:

1. An active tank stabilizer adapted for using ballast liquid means for stabilizing the hull of a marine vessel against rolling comprising:

first and second active tank means respectively disposed at opposite sides of said hull and adapted for containing said ballast liquid means,

ballast liquid transfer means coupling said first and said second active tank means and having an elongate transfer portion extending transverse of said hull, and motive means for transferring said ballast liquid means from one to the other of said active tank means through said ballast liquid transfer means,

said elongate transverse portion of said ballast transfer means being located substantially higher in said hull than said active tank means so that the static and dynamic moments exerted by said liquid ballast means on said hull are additive.

2. Apparatus as described in claim 2 wherein said elongate transverse portion of said ballast transfer means is located substantially vertically above said active tank means with respect to said hull for the purpose of exerting additive static and dynamic stabilizing torques on said hull about the roll axis thereof.

3. Apparatus as described in claim 1 wherein said elongate transverse portion of said ballast transfer means is off set horizontally in the fore-aft direction with respect to said active tank means for the purpose of exerting stabilizing torques on said hull about the yaw axis thereof.

4. Apparatus as described in claim 1 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means and off set horizontally in the fore-aft direction with respect thereto for the purpose of simultaneously exerting stabilizing torques on said hull about the roll axis thereof and about the yaw axis thereof.

5. Apparatus as described in claim 1 wherein said means for transferring said ballast liquid means com prises:

inertial reference means,

said motive means being under control of said inertial reference means for transferring said ballast liquid means from one to the other of said active tank means through said ballast transfer means.

6. Apparatus as described in claim 5 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means.

7. Apparatus as described in claim 6 wherein said elongate transverse portion of said ballast transfer means is located substantially vertically above said active tank means with respect to said hull.

8. Apparatus as described in claim 6 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means and off set horizontally with respect thereto in the direction of the longitudinal axis of said hull. 

1. An active tank stabilizer adapted for using ballast liquid means for stabilizing the hull of a marine vessel against rolling comprising: first and second active tank means respectively disposed at opposite sides of said hull and adapted for containing said ballast liquid means, ballast liquid transfer means coupling said first and said second active tank means and having an elongate transfer portion extending transverse of said hull, and motive means for transferring said ballast liquid means from one to the other of said active tank means through said ballast liquid transfer means, said elongate transverse portion of said ballast transfer means being located substantially higher in said hull than said active tank means so that the static and dynamic moments exerted by said liquid ballast means on said hull are additive.
 2. Apparatus as described in claim 1 wherein said elongate transverse portion of said ballast transfer means is located substantially vertically above said active tank means with respect to said hull for the purpose of exerting additive static and dynamic stabilizing torques on said hull about the roll axis thereof.
 3. Apparatus as described in claim 1 wherein said elongate transverse portion of said ballast transfer means is off set horizontally in the fore-aft direction with respect to said active tank means for the purpose of exerting stabilizing torques on said hull about the yaw axis thereof.
 4. Apparatus as described in claim 1 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means and off set horizontally in the fore-aft direction with respect thereto for the purpose of simultaneously exerting stabilizing torques on said hull about the roll axis thereof and about the yaw axis thereof.
 5. Apparatus as described in claim 1 wherein said means for transferring said ballast liquid means comprises: inertial reference means, said motive means being under control of said inertial reference means for transferring said ballast liquid means from one to the other of said active tank means through said ballast transfer means.
 6. Apparatus as described in claim 5 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means.
 7. Apparatus as described in claim 6 wherein said elongate transverse portion of said ballast transfer means is located substantially vertically above said active tank means with respect to said hull.
 8. Apparatus as described in claim 6 wherein said elongate transverse portion of said ballast transfer means is located above said active tank means and off set horizontally with respect thereto in the direction of the longitudinal axis of said hull. 